The present invention relates to systems and methods for polarization modulation of an optical signal. More specifically, the present invention relates to the design and methods of operation of a laser source and laser projection system to reduce the presence of speckle that may be visible in a laser projection image. Speckle may result whenever a coherent light source is used to illuminate a rough surface, for example, a screen, or any other object that produces a diffused reflection or transmission.
Particularly, a multitude of small areas of the screen or other reflecting object scatter light into a multitude of reflected beams with different points of origination and different propagation directions. At an observation point, for example in the observer's eye or at the sensor of a camera, these beams interfere constructively to form a bright spot, or destructively to form a dark spot, producing a random granular intensity pattern known as speckle. Speckle may be characterized by the grain size and contrast, usually defined as a ratio of standard deviation to mean light intensity in the observation plane. For a large enough illuminated area and a small enough individual scattering point size, the speckle will be “fully developed,” with a brightness standard deviation of 100%. As an example and not a limitation, if an image is formed on a surface screen using laser beams, such granular structure will represent noise, or a serious degradation of the image quality.